1. Field of the Invention
The present invention relates to a vehicular remote control device for controlling operation of a vehicle-mounted device based on a trigger signal from a predetermined switch operated by an operator such as a driver. The present invention also concerns a method of such remote control, and more particularly relates to a method of operating a vehicular remote control device for controlling transmission of a request signal when the request signal is transmitted from a transmitting unit of a vehicle-mounted device to a portable unit carried by the operator, based on input of a trigger signal from a predetermined switch of the vehicle, such as a door locking switch operated by the driver.
2. Description of the Related Art
Japanese Laid-Open Patent Publication No. 11-131884 discloses a conventional technology relating to a vehicular electronic key system, which initiates communications between a portable unit carried by an operator such as a driver and a vehicle-mounted device, based on a trigger signal serving as an activation signal output from a switch operated by the operator, which is disposed on the outer door handle or trunk lid of the vehicle, and which unlocks the doors when an ID transmitted from the portable unit to the vehicle-mounted device successfully matches an ID stored in the vehicle-mounted device.
In Japanese Laid-Open Patent Publication No. 11-131884, the vehicle-mounted device transmits a request signal from the transmitting unit thereof to the portable unit based on input of the trigger signal that requests transmission of a response signal including the ID. In this case, the vehicle-mounted device has a timer circuit for preventing the battery thereof from running out due to successive transmissions of request signals based on successive operations of the switch by the operator. Therefore, when the vehicle-mounted device has been operated for a time preset in the timer circuit, the vehicle-mounted device becomes idle regardless of whether the trigger signals are input or not, whereby transmission of the request signal is prohibited.
In such a system, if the trigger signal is input into the vehicle-mounted device every time that the operator operates the switch, the transmitting unit transmits a request signal to the portable unit every time that the trigger signal is input. As a result, since the total transmission time of the request signal becomes long during the predetermined period, the temperature rises inside the transmitting unit due to transmission of the request signal, which adversely affects the performance of the transmitting unit.
In addition, because the preset time is set in order to prevent the battery from running out, even when the total transmission time within the predetermined period of time is shorter than the preset time, a rise in temperature inside the transmitting unit may still adversely affect performance of the transmitting unit, before the timer circuit prohibits transmission of the request signal based on the preset time.
A predetermined waiting time between communication sequences between the vehicle-mounted device and the portable unit may be one option for limiting successive transmissions of request signals as a result of successive switching operations caused by the operator. Such a countermeasure, however, could decrease the merchantability of the vehicle-mounted device.
If a device that lowers the transmission level of the request signal is installed in the transmitting unit, for suppressing a rise in temperature thereof, the vehicle-mounted device may become prohibitively expensive.